Do you have others you could post? I'm trying to look at the ambient vs. background but it looks like the natural shadows fall in roughly the same area as where the line is so it's hard to tell if that was a mechanical error in your camera or something with the processing.

Yes Kodachrome does need to be reexposed but AFIK the lights are all colored to develop the different bases, and it is reexposed in between the development stages of different layers of the film (develop, expose, develop, expose...). So I would expect a reexposure error to have a heavy color cast.

Also, what kind of camera were you using? Were you using something with a vertical traveling multiblade shutter or a side curtain shutter like a Pentax K1000?

__________________________________________________ ____________________________________________Yes, it was shot with a K1000. Using a Vivitar 283 on camera. If I remember correctly, I was using 60th for shutter speed (for ambient sunny behind)(max shutter sync speed on k1000) and aperture for flash fill.

I might have accidentally set it at 1/125th or so, its my bad. I've just never had this happen before at all. But since it is in the same place in every frame, I guess it was my bad after all. Oh well, live and learn
here are some more.